Physical mechanisms of conduction-to-keyhole transition in laser welding and additive manufacturing processes

Thermo-hydrodynamic phenomena which take place during laser welding or additive manufacturing processes as powder bed fusion, have been investigated for years, but recent advances in X-ray images and situ analysis highlighted new findings that are still under debate. Conduction-to-keyhole transition, more broadly, keyhole dynamics, typical cases, where complex coupling between hydrodynamic optical problems involved. In this paper, a melt pool model is developed with the software COMSOL Multiphysics®, energy deposition computed self-consistently thanks to ray tracing algorithm. The successfully reproduces experimental published literature helps analyze accurately role played by beam trapping phenomenon conduction-to-keyhole both spot (i.e., stationary illumination) configurations scanning speed). particular, it shown depending on speed, multiple reflections might be either stabilizing destabilizing factor. Understanding these mechanisms thus prerequisite controlling stability of pools joining processes.